TEMPERATURE DEPENDENCE OF THE EXTRAORDINARY HALL EFFECT IN AMORPHOUS ( FeCoNi)78B12Si10 ALLOYS

Abstract

Temperature dependences of the extraordinary Hall coeficient R, and resistivity p, yield amp2 (arising from the side-jump mechanism) for the majority of investigated FeCoNi-based alloys. The deviation from p2 variation in Co-rich alloys is probably due to the temperature dependence of the magnetic anisotropy in these alloys. One of the characteristic features of amorphous ferromagnetic alloys, as compared to the crystalline ones, is large extraordinary Hall effect. This is a di- rect consequence of the high resistiGty p of these al- loys. It is generally accepted (l, 21 that in strongly dis- ordered transition metal alloys the main contribution to the extraordinary Hall effect comes from the side- jump mechanism (3) that leads to the p2 dependence of the extraordinary Hall coefficient R,. The experimen- tal confirmation of this dependence is somewhat diffi- cult in amorphous alloys because their resistivity, that is already large, changes only slightly with tempera- ture, and the same holds for R, too. Therefore very accurate determination of R, is required in order to deduce the correlation between R, and p. Here we re- port this correlation for amorphous FexNi.ra-xBlzSilo, FexCo78-xB12Si1~ and C0~Ni78-~B12Si10 alloys. All our alloys are ferromagnetic with the Curie tempera- ture Tc above 420 K except for Fe23Ni~~B12Si10 and alloys (Tc=410 and 390 K respec- tively). The Hall resistivity p~ (in magnetic field up to 1 T) and electrical resistivity have been measured from 77 to 420 K. The details concerning the sample prepa- ration and the measurement technique were reported earlier (4, 51. The temperature variations of the resis- tivity were reported in reference (6). The rather small cross section of our samples (typically 0.8 x 0.018 mm2) resulted in an uncertainty of about 10 % in the abso- lute value of OH. The initial slopes of the Hall resistivity as a func- tion of magnetic field RH= (A~H/AB)~=~ for all our alloys are of the order m3 A-' s- . At the same time the n~rmal Hall coefficient & of the amorphous alloys is equal to or lower than the free electron value and is practically temperature independent. For our s and alloy systems & is of the order 10-lo m3 A-' therefore we neglect its contribution to RH. Hence RH is practically equal to R. (po AM/AB)B=, where M is the magnetization of the sample. In the case of a thin Hall sample and isotropic material